The screen printing industry has grown tremendously over the last few decades. Various garments such as jackets, sweat shirts and other textile substrates are screen printed to place various indicia upon the substrate. The typical prior art apparatus used, whether on the single or multiple station type, include a planar pallet upon which the garment is positioned and an open frame which is pivoted at an inboard or rearward point between an open position allowing the garment to be mounted on the pallet and a closed position engaging the peripheral edge of the pallet to secure the garment upon the pallet prior to moving the printing screen carrying the selected indicia into contact with the garment. The general operation of this type of screen printing apparatus is well-known in the industry.
The inner peripheral edge of the open retaining frame typically is provided with a resilient seal which frictionally engages the portion of the garment overlying the surrounding edge of the pallet to grip the garment material between the seal and the outer edge of the pallet to pull it tightly over the planar surface in a taut condition to accept the screen printing without subsequent distortion after removing the garment.
The retaining frame is pivoted to a support frame or the base of the printing apparatus at its rearward end so that the opposite or forward end is open and free from obstruction to permit the garment to be mounted on the pallet. Typically, the print screen and its associated ink holder and squeegee applicator are similarly pivoted in an independent manner at the inner end to be moved into engagement over the pallet after the retaining frame is moved into its closed position. Typical examples of such screen printing apparatus include those commercially available and sold by Richardson Industries located in Columbus, Ohio under the tradenames Richardson-66, Model 8800 and Apex-64 carousel type printers.
One of the problems associated with the conventional construction of prior art retaining frames is the very significant force required to move the retaining frame to its final closed position about the rearwardly located hinge point. The frictional resistance which pulls the material taut between the retaining frame seal and the outer edge of the pallet is the greatest at this point.
While this is not an insurmountable problem in a manually operated construction, wherein the final closing force is manually applied to the outer end of the retaining frame, it has been a significant deterrent to automating or constructing a mechanically powered retaining frame assembly because the forward or outer end of the pallet must be free and open to allow convenient loading of the garments onto the pallet. Further, locating a power piston or equivalent driving means at the inner end near the pivot axis of the retaining frame has not been practical because of the very significant force required to fully close the frame over the pallet. The disadvantageous leverage involved in the conventional construction would require a linear actuator too large to be economically practical.
Prior to the present invention, a practical and efficient mechanically automated screen printing retaining frame construction has eluded those skilled in the art in spite of the desirability of such a feature to increase productivity and convenience of the operation.